uniform sampler2D cdf;
vec4 dataInterpolation( sampler3D data, const vec3 texCoords ) {
   //return texture3D( data, texCoords ); 
   vec4 v = texture3D(data, texCoords);
   vec2 lookupCoord = vec2(v.a, 0.9);
   vec4 lookupValue = texture2D(cdf, lookupCoord);
   vec4 result = vec4(lookupValue.r, lookupValue.r, lookupValue.r, lookupValue.r);
   return result;
}


